In recent years, cathode-ray tubes (CRTs) has been replaced by rapidly-spreading active matrix display devices, as typified by liquid crystal display devices and organic EL display devices, in which active elements such as TFTs are used, and the active matrix display devices have been widely used in televisions, monitors, cellular phones, etc. by utilizing their features of energy saving, thinness, lightweight, etc.
Among them, electronic apparatuses including small-to-medium-sized display devices, such as cellular phones and PDAs (personal digital assistants) in particular, have started to adopt a gate driver monolithic (GDM) technique based on amorphous silicon for reduction in cost.
For example, Patent Literature 1 discloses a liquid crystal display device including: pixel transistors provided in a display region of the liquid crystal display device; and a gate drive circuit (gate driver), provided in an area around the display region, which includes transistors, the pixel transistors and the transistors being monolithically formed by using an identical amorphous silicon layer.
FIG. 10 is a plan view showing the gate drive circuit of the liquid crystal display device and a wiring region of the gate drive circuit.
As shown in FIG. 10, in the right edge region of the drawing, i.e., in a region (not illustrated) adjacent to the display region of the liquid crystal display device, there are provided driving transistors for driving shift registers. On the other hand, in the left edge region of the drawing, i.e., in a region farthest from the display region, there is provided a wiring region where there are provided a plurality of main wires 150 through which signals are applied to the shift registers.
Further, in the intermediate region of the drawing, i.e., in a region between the wiring region and the region where the driving transistors are provided, there are provided control transistors for the shift registers.
It should be noted that branch wires 160 electrically connecting the main wires 150 and the driving transistors of the shift registers and branch wires 160 electrically connecting the main wires 150 and the control transistors of the shift register are formed by a different layer from the main wires 150. In the configuration of Patent Literature 1, the main wires 150 are formed by the same layer as a pattern of gate wires and gate electrodes, and the branch wires 160 are formed by the same layer as a pattern of data wires and source electrodes.
Further, an electrical connection between the control transistors, an electrical connection between the driving transistors, and an electrical connection between the control transistors and the driving transistors are made by using the same layer as the main wires 150 or the same layer as the branch wires 160.
FIG. 11 is a cross-sectional view, taken along the line G-H of FIG. 10, which shows the appearance of an area of connection between a main wire 150 and a branch wire 160.
As shown in FIG. 11, the main wire 150 is provided on an insulating substrate 170, and the branch wire 160 is provided on a gate insulating film 180 formed in such a way as to cover the main wire 150 and the insulating substrate 170.
Furthermore, there is a passivation film 190 formed in such a way as to cover the branch wire 160 and the gate insulating film 180.
There is a first contact hole 200, which is a hole formed both in the gate insulating film 180 and the passivation film 190 so that part of the main wire 150 is exposed. On the other hand, there is a second contact hole 210, which is a hole formed in the passivation film 190 so that part of the branch wire 160 is exposed.
As shown in FIGS. 10 and 11, the main wire 150 and the branch wire 160 are electrically connected to each other through a connection conductor 220 formed both in the first contact hole 200 and the second contact hole 210, i.e., through the same layer as pixel electrodes electrically connected to drain electrodes of the pixel transistors provided in the display region of the liquid crystal display device.
Patent Literature 1 states that the foregoing configuration allows the gate drive circuit and its wires to be formed at the same time as the display region by directly using the step of forming the display region of the liquid crystal display device, and as such, can integrate the gate drive circuit and its wires without adding a separate manufacturing step, thus achieving a reduction in manufacturing cost.